[unreadable] While functional correction of genodermatoses has been demonstrated using retroviral mediated ex-vivo gene therapy, the cost and traumatic features of this procedure has led to the search for additional non-viral technologies for gene therapy. Non-viral vector gene transfer vectors have been plagued by the inability to get both therapeutic and persistent levels of gene expression in vivo. We have recently described a non-viral vector system based on DNA transposons that integrates an expression cassette into the chromosomal DNA of hepatocytes in vivo. Stable gene transfer is achieved by transient expression from the transposase gene resulting in the integration of transposon DNA flanking an expression cassette. As a result, life-long and therapeutic concentrations of human factor IX have been achieved in hemophilia B mice. Moreover, there is no toxicity and secondary transposition if it occurs is extremely rare. The two major limitations of this system are the limited gene transfer capacity (-5.0 kb), and the efficiency of integration, which is ~5% of transfected: hepatocytes in vivo and varies between different cell types in culture. While the effectiveness of this transposon has been demonstrated for diseases like hemophilia, there are other diseases in which the efficiency and size of the -DN A insert will need to be increased. We have made progress in that we have identified hyperactive transposase mutants that are >8x more efficient than the original transposase that in Combination with a new transposon increases integration by 14x and allows for efficient transposition of DNA molecules of at least 14 kb. We have recently shown that transposon-based vectors work well in skin models and plan to test current and newly obtained hyperactive transposons hi skin models of gene transfer. Moreover, we will use our new chimeric transposase-helper dependent adenoviral vector system in preclinical gene therapy studies. [unreadable] [unreadable]